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HIDRAULIC HAMMER EXCAVATOR FAILURE DUE TO SOLID PARTICLE CONTAMINATION Mitar T. Jocanović a, Velibor V. Karanović b, Andrea V. Ivanišević a, Darko M. Knežević b a University of Novi Sad, Faculty of Technical Sciences,

Department of Industrial Engineering and Management, b University of Banja Luka, Faculty of Mechanical Engineering,

Department of Automation and Mechanisation, Bosnia and Herzegovina, Republic of Srpska

Summary: Hydraulic systems of mobile machines are often contaminated by

solid particles. Solid particles increase the abrasive wear intensity of hydraulic components and present one of the main causes of system failure. The paper presents a representative example of the solid parti-cle influence on the wear intensity of hydraulic hammer parts, in the cement industry environment.

Ključne reči: particles, excavators, hydraulics, wearing.

Introduction ontamination of the working fluid of a hydraulic system is one of the biggest enemies of mobile machines. In mobile machines

that are mostly used in dirty environments, it is necessary to protect the hydraulic system by proper designing, especially in respect of external contamination.

The influence these contaminants have on operation and reliability of hydraulic components and therefore of hydraulic systems as well, may significantly decrease the planned exploitation life (Fitch, 1988), (Bioča-nin, Pavlović, 2011, pp.106-130), (Guberinić, Milojević, 2009, pp.31-45). Whether their state of matter is gas, liquid or solid, contaminants repre-sent one of the factors that has the biggest impact on failures of hydraulic system components (Liang, et al, 1999, pp.278-298). Solid particles have a significantly destructive character compared to other contaminants (Chandrasekaran, et al, 1985, pp.219-222), (Lehner, Jacobs, 1995, pp.261-276), (Odi-Owei, Roylance, 1986, pp.239-255), (Williams,

C

DOI: 10.5937/vojtehg62-4676

FIELD: Mechanical Engineering ARTICLE TYPE: Original Scientific Paper

e.mail: mitarj@uns.ac.rs

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Hyncica, 1992, pp.57-74) and they express it through a mechanism of abrasive and erosive wear (Fitch, Hong, 2004). Solid particles may get into a hydraulic system from the environment in which such a system operates (external contamination) or through internal contamination that is the result of the presence of solid particles in hydraulic fluid (so called “built-in” contamination), or as a result of the wear of operating parts of hydraulic components (Fitch, Hong, 2004).

Problems with using different fluids in hydraulic systems as well as the significance of decreasing the contaminants with regards to proper operation of a hydraulic system have been analyzed through various tests and applied to certain hydraulic components (pumps, valves, etc) (Totten, De Negri, 2011). In addition, the impact of contaminants, in the form of solid particles, on the wear of hydraulic components and systems was monitored through various tests carried out on certain components. It was also proved that solid particles cumulate in clearan-ces of operating components, creating layers of contaminants that may lead to partial or total failure of a hydraulic system component (Jocano-vić, 2010).

Because of the above mentioned reasons and in order to prevent the increase of total production costs as well as to increase the reliability and efficiency, in modern automatized technological systems it has been insisted on the introduction of system condition monitoring which is the integral part of the preventive and proactive maintenance strategies (Jo-canović, et al, 2012, pp.281-288). One should also bear in mind that re-quests for using the assets, measuring and other equipment needed for carrying out the condition monitoring, need to be valid from the aspect of rentability or, in special circumstances, from the aspect of reliability, re-gardless of the maintenance expenses and complexity of the technical system (for example military applications and the like).

This paper presents the impact of the contamination of working fluid in the excavator hydraulic system through an operating part – hydraulic hammer. It was noticed that due to the inappropriate design of the ham-mer and a wrong selection of the return filter in the excavator hydraulic system, during the operation, solid particles as contaminants penetrate inside the hydraulic system and increase the wear of the operating parts of hydraulic components (primarily the operating of the hydraulic pump), as well as the operating parts of the hydraulic hammer. For better under-standing of the impact of hydraulic oil contamination with solid particles, this paper also includes a photo-documentation of critical parts of certain components that were damaged. In addition, a financial analysis was al-so carried out, which justifies the investment in equipment and additional filtering on machines that work in specific conditions.

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Description of the Operation of a Hydraulic Hammer System A hydraulic hammer system, shown in Figure 1, receives the working

fluid from the pressure line of the central system “P” that is connected with a double piston axial pump with a capacity of 315 l/min. The directional control valve 9/3 (position 1), supplies the hydraulic hammer with the working fluid (position 10) by bringing the control pressure to 1a side of the directional con-trol valve. Through a group of regulating valves (positions 3 and 5) and the pressure line labeled with “I”, the oil under pressure supplies the entrance side of the hammer regulating valve (position 10) which further distributes the working fluid according to the phases of hammer operations. The hydraulic accumulator (position 9) decreases the occurrence of hydraulic shocks and pulsations of pressure while the hammer is operating. The oil from the ham-mer returns directly to the reservoir of the excavator hydraulic system thro-ugh the return line “O”, the directional control valve 7 and the return filter 6.

P P

R

R C C

1a 1b

2 3

4 5

6

7 8

9

10

I

O

Figure 1 – A part of the hydraulic scheme for the operation of the hammer

Slika 1 – Posmatrani deo hidraulične šeme čekića

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The cross-sectional view (Figure 2) illustrates the operation of the hydraulic hammer which is performed in phases as follows:

• Phase 1: The working piston (P) moves upwards. The hydraulic oil from the pressure line enters the chambers labeled

by positions 11 and 18. The regulating valve (19) is pushed into the lower end position. The hammer working piston moves upwards compressing the gas into the compression chamber (15). The working fluid from chamber 14 is released towards the chamber (17) through the hole in the regulating valve (19), and from there, the oil is sent directly to the reser-voir through the return line and the filtering system.

• Phase 2: Setting the regulating valve (19) in the upper position. When the oil under pressure is pushed into the chamber (11), the ham-

mer working piston moves upwards to the position when the chambers (12) and (16) are filled with oil. At the moment when the pressures are equal due to the difference in the surfaces affected by the pressure, the regulating valve (19) moves into the upper end position joining the chambers (18) and (14).

• Phase 3: The working piston moves downwards When the chambers (14) and (18) are joined, the force which acts on the

upper ring-shaped surface of the working piston in the chamber (14) together with the force created by the compressed gas the storage space of the cham-ber (15) moves the hammer working piston (P) into the lower working position.

• Phase 4: The working piston hits the chisel When moving downwards, the working piston (P) hits the chisel (20).

At that moment, the middle part of the piston joins the chambers (12) and (13) and, as a result, the chamber (16) on the lower side of the regulating valve (19) unloads as well. The force on the lower side of the regulating valve is smaller than on the upper side causing the regulating valve to return to the lower end position.

15

14

11

12

15

14

12 13

16

18 17

18 18

16

18

INPUT OUTPUT

INPUT OUTPUT

INPUT OUTPUT

INPUT OUTPUT

19

20

P

Phase 1 Phase 2 Phase 3 Phase 4

19

Figure 2 – Crossectional view of the hydraulic hammer and the operational phases

Slika 2 – Presek hidrauličnog čekića i njegove radne faze

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The given description presents one operating cycle of the hydraulic hammer. The operating process of causing the hits of the hammer requires continuous repetition of the previously described cycle. From the afore-mentioned, it can be noticed that the operation of the hydraulic hammer represents a dynamic cycle of movements of certain hammer parts which, in order to work properly, also require certain conditions for long-term ex-ploitation. One of such conditions is also keeping the working fluid clean.

Causes of Contamination in the Excavator Hydraulic System In the excavator hydraulic system, it was visually noticed that, due to

poor filtering of the filter block (Figure 1 – position 6) used in the excava-tor return line, the color of the hydraulic oil changes due to the presence of solid particles of cement dust, which affects the work and reliability of the excavator during the exploitation. Frequent failures of certain compo-nents in the system were noticed (of proportional and servo type). In or-der to prove the assumption relating to inadequate filtering, oil samples were taken from the reservoir (a reservoir volume of 250 liters) of the hy-draulic excavator that had been exploited for 950 work hours. By imaging the content of solid particles in oil mass with a device type FCU 2045 HYDAC (Hydac International GmbH., 2010), we obtained the information about the oil purity class (Table 1).

By monitoring the contamination with solid particles, it is crucial to define the sources of contamination, and later, to spot and correct possi-ble mistakes which cause contamination. When the filtering in the system is not appropriate, it generally leads to a constant increase of contami-nants in the form of solid particles in the working fluid of the hydraulic system. In the case of an excavator, there were three basic causes of contamination of the working fluid.

Table 1 – Content of solid particles in the oil mass of the excavator hydraulic system

Tabela 1 – Sadržaj čvrstih čestica u uljnoj masi hidrauličnog sistema bagera

Number of operating hours [h]

Number of measured solid particlesby size in the 100 ml sample

Purity class Description and the

number of the sample excavator oil 2 μm 5 μm 15 μm 25 μm NAS 1638

ISO4406/88

Before filtering (1) 950 950 >>> 8,585.215 1,605.631 1,327.103 >15 24/23/21

>>> – too many particles immeasurable by the device

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The executive part of the excavator hydraulic system, i.e. the ham-mer, was noticed as the first source of contamination (of an external cha-racter) during the monitoring process. Through the operating parts of the hammer, due to a mistake in the design (a poor sealing system), there is a penetration of a big quantity of solid particles washed down by the wor-king fluid and distributed in the hydraulic system through the return line into the reservoir of the working fluid.

The second source of contamination (of an internal character) is the inadequate solution for filtering the working fluid in the return line of the hydraulic hammer system. With regards to the filter construction, the degree of the filtration rate is βx=200 for 30 µm particles. However, the system has a built-in axial piston pump with the LS regulation and the group of proportio-nal and servo valves for the operation of which one needs to provide filters with a degree of fineness between 2 and 5 µm in line with the old ISO 4406/87, or 4 and 6 µm(c) in line with the new ISO 4406/99 standard.

The third cause of contamination is the inadequately designed system of the hammer return line, especially the filter block (Figure 1 - position 6). During the monitoring process, it was noticed that there were some sudden rises of pressure in the filter housing which causes the tearing of the steel filter mesh (Figures 3 and 4) and the penetration of filth in the form of solid particles.

Figure 3 – Filter cartridge embedded in the return line of the hydraulic hammer system

Slika 3 – Filterski uložak, ugrađen u povratnom vodu hidrauličnog sistema čekića

Figure 4 – Visible damage in the steel mesh and the filter medium

Slika 4 – Vidljiva oštećenja na čeličnoj mrežici filterskog uloška

In order to prove the previously mentioned facts, the contamination of

the new fluid was measured before the system was put into operation and after a certain period of exploitation, and the measuring results are presen-ted in Table 2. We also need to mention that filtering was executed with external, i.e. a secondary filtering system, and that the samples were taken from the reservoir in line with the prescribed sampling method.

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Table 2 – Results of measuring solid particles in the excavator working fluid mass after oil change

Tabela 2 – Rezultati merenja čvrstih čestica u hidrauličnom sistemu bagera nakon zamene ulja

Number of operating hours

[h]

Number of measured solid particles by size in the 100 ml sample Purity class

Description and the

number of the sample Exca-vator

New oil 2µm 5 µm 15 µm 20 µm NAS 1638

ISO 4408/87

After filtering the new oil (2)

950 0 168.887 16.767 112 49 7 18/16/10

During the operation (3)

985 35 2.752.511 163.839 2.159 1.847 10 21/18/13

During the operation (4)

1230 280 4.227.071 1.261.567 34.047 37.375 13 23/21/17

As it can be noticed, the content of contaminants in the form of solid

particles in the working fluid increased from satisfying purity class NAS 7 to unpermitted class NAS 10 for a very short period of operating time (35 hours) of the excavator in the extremely contaminated environment (ce-ment industry environment). After 280 operating hours, the oil purity class increased to NAS 13 which represented a class of contamination at un-permitted level (Figure 5).

Num

ber

of p

artic

les i

n 10

0 m

l oil

2 μm

5 μm

15 μm

20 μm

[hour] Figure 5 – Increase in the oil contamination level in 280 operating hours

Slika 5 – Povećanje kontaminacije ulja za 280 radnih časova

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Since the excavator was within the warranty period, there was not any possibility to make any change on the hydraulic excavator system in agre-ement with the servicing staff. The servicing staff insisted that both oil and filters were supposed to be replaced even before the prescribed terms (prescribed replacement of filters after 1000 hours; changing oil after 5000 operating hours), ignoring the presented observations and reports relating to the operation and contamination of the working fluid in the hydraulic ex-cavator system. It is also important to mention that during 1230 hours of the excavator operation, there were three replacements of filters in the hammer return line and one complete change of oil at 950 working hours.

Influence of Contaminants on the Damage of Hydraulic Excavator Components

Research on the negative impact of contaminants in the form of solid pa-rticles was done on a new excavator the exploitation life of which ended after only 1230 operating hours. Because of the inadequately designed hydraulic system, as well as due to a mistake in the design of the excavator hammer, the penetration of contaminants (particles originating from SiO2, MgO, CaO3, Al2O3) into the hydraulic system was at a very high level. The role of the filter in the system may be neglected because the filter did not do the work which, according to the system functioning plans, it was supposed to do.

Due to a poor design of the hammer sealing system, where there is only one seal for dust removal (Figure 6 – position 47), a great quantity of solid particles from the atmosphere of the cement industry work environ-ment penetrated the housing of the hammer (Figure 6 – position 1). Solid particles that penetrated the interior of the hammer were washed down by the working fluid and sent to other parts of the hydraulic system, all the way to the reservoir, and after that the pump sent them again to the execu-tive part and other components of the excavator hydraulic system. In this way, the level of contamination cyclically increased in the working fluid.

Due to the penetration of solid particles into the housing, damage occurred in the form of metal particles, as in Figure 7 which presents the interior of the hammer housing (Figure 6 - position 1) with the products of wear that occurred as a result of primarily abrasive wear and partially due to vibration. Figure 8 shows an enlarged image of the housing with the presence of particles and Figure 9 shows the assembly of the piston and the housing with the presence of accumulated solid particles after disas-sembling the hydraulic hammer. In the presented housing (Figure 9), there is a driving part of the hammer piston (Figure 6 - position 12) which is also presented in Figure 10 with visible traces of abrasive wear result-ing from the performance of solid particles from the environment. Due to

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the presence of contaminants, significant damage is visible on the ham-mer piston in the form of longitudinal scratches that occurred as a result of the abrasive impact of solid particles present in the oil and vibrations that occurred during the operation of the hammer.

Figure 6 – Explosion scheme of the hydraulic hammer

Slika 6 – Detaljna šema hidrauličnog čekića

Figure 7 – Housing of the hammer with particles

Slika 7 – Kućište čekića sa vidljivim čvrstim česticama

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Figure 8 – Enlarged image of the housing with the mass of metal particles Slika 8 – Uvećan prikaz kućišta sa metalnim česticama

Figure 9 – The assembly of the housing and the piston of the hammer with solid

particles Slika 9 – Sklop kućišta i klipa hidrauličnog čekića sa vidljivim čvrstim česticama

Figure 10 – Abrasive damage on the hammer piston

Slika 10 – Abrazivna oštećenja na klipu čekića

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Solid particles present in the working fluid also caused the abra-sive wear damage on the piston of the hammer regulating valve (Figure 6 – position 70) and it is shown in Figure 11.

Figure 11 – Abrasive damage of the regulating valve piston Slika 11 – Abrazivna oštećenja na klipu regulacionog ventila

Besides the presented parts of only one operating assembly of the

hydraulic hammer system, the hydraulic excavator system also had da-mage on other components, primarily on the axial piston pumps with the LS regulation as well as on the proportional control valves. On the basis of the detailed analyses of the damage causes, on the filter and other hydraulic components, we came up with an idea to use the equipment for monitoring the basic physical values (pressure, flow and temperature) in the return line and, based on these values, to state the cause of the mechanical failure of the filter cartridge.

Monitoring the Hydraulic Hammer System In the hydraulic hammer system, on the return line that takes the oil

out of the hammer housing through the filter block (Figure 1 - position 6), the sensors for measuring the pressure (Figure 12) were set up on the measuring points M1 and M2. Based on the measured values obtained through the multy handy diagnostic unit 2045 (Hydrotechnik UK, 2012), it was determined that when the hammer chambers 12, 13 and 16 were un-loaded in phase 4 (Figure 2), the pressure dropped in the return line bet-ween the inlet (M2) and the outlet (M1) of the filter housing, to the value of ∆p=3.5 bars (Figure 13). According to the manufacturer’s recommenda-tion, the pressure relief valve embedded in the housing of the filter was adjusted to open after the pressure had reached the value of ∆pmax=1.5 bars. Due to the impact of variable pressure values of ∆p=3.5 bars on the filter cartridge, or more specifically on the mesh and the filtering medium,

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enormous force was generated leading to bending and twisting of the me-dium and steel protection of the filter cartridge. Due to the cyclic loading, the steel mesh became worn out and torn and the filter cartridge medium was splitted (Figures 3 and 4). This phenomenon was also identified after replacing the old filter cartridge with a new one. After only 250 operating hours, the same phenomenon and the damage happened again. Due to mechanical damage, the filter cartridge no longer performed its role and the contaminants that passed through clearances between the seals and the working piston went directly into the reservoir of the hydraulic system.

M1 M2

Figure 12 – Measuring points in the filter block of the hydraulic hammer system return line Slika 12 – Merna mesta na filterskom bloku u povratnom cevovodu hidrauličnog sistema

Pressure before the filter Pressure after the filter

Figure 13 – Changes of pressure values in the filter block of the hammer return line

Slika 13 – Izmerene promene pritiska na filterskom bloku After the monitoring process, the main cause of damage in the filter

cartridge was determined and after that the source of contamination of the whole system was determined as well.

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The solution to the problem was achieved in agreement with the ex-cavator supplier who performed an adequate replacement of damaged components in the hydraulic system and fixed the defect in the hammer return line filter block by installing a filter with appropriate fineness of 4 µm(c) and by setting the pressure relief valve in the filter block to the va-lue of 1.5 bars. In addition, the hammer was replaced with another ham-mer with an appropriate structural design with an improved sealing system that prevented the excessive penetration of solid particles into the interior of the hammer. Also, a secondary filtering system was installed on the main reservoir of the hydraulic excavator system, with the capacity of 10% of the capacity of the main hydraulic pumps. A permanent solu-tion was thus provided for additional filtering of the hydraulic working fluid and for keeping its pureness at the required level.

Techno-financial Analysis of the Breakdown Due to the breakdown that occurred in the hydraulic system, the main

cause of which was the excessive contamination with solid particles and im-proper filtration, the user of the excavator filed a claim for a replacement of components in the whole hydraulic excavator system. In negotiations with the manufacturer, after submitting adequate evidence, an agreement was reached to do so. Table 3 shows the costs of the new hydraulic hammer and the replaced hydraulic excavator system without executive elements (hydraulic cylinders were not replaced), as well as the costs of the secondary filtering system with a counter of solid particles and a sensor for measuring moisture in the oil mass that may timely signalize the operator when the level of contamination with solid particles in the system increases so that he/she may respond in time. Normally, the secondary system does not have to be connected to the hydraulic system all the time; it is used from time to time, for a certain number of operating hours, in order to separate the contaminants in the form of water and particularly solid particles.

Table 3 – The price of the equipment installed in the hydraulic excavator system

Tabela 3 – Cena opreme ugrađene u hidraulični sistem bagera

No. Component type Quantity Costs (EUR) 1. Hydraulic blocks with a set of regulating valves

for controlling the power employed for movement, rotation and operation of the excavator arm

5 blocks 128,412.00

2. Set of two axial piston pumps with the LS regulation 2 pieces 15,560.00 3. Hydraulic drive motors for movement and rotation

with the associated regulating valves in the block 3 pieces 24,954.00

4. Hydraulic hammer 1 piece 29,530.00 TOTAL: 198,456.00

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No. Component type Quantity Costs (EUR) 1. Secondary filtering system with two filters of big

capacity (pump capacity 25 liters/minute and filtration rating βx=200 size 14 and 4 μm(c).

1 piece 2,875.00

2. Device for measuring solid particles and the moisture sensor

1 piece 4,870.00

3. Price of the spare filter 14 or 4 μm(c). 1 piece 200 TOTAL: 7,945.00

Table 4 presents the financial analysis of all expenses relating to the breakdown, maintenance and repair of the excavator as well as the ratio of losses of the excavator owner and manufacturer.

Table 4 – The Cost analysis review

Tabela 4 – Analiza troškova Calculation

element Amount (EUR)

Note

Basic income parts of the excavator operation 1. Total cost of the excavator

with a hammer 550.000,00

2. Annual income of the excavator with full operating hours

Number of operating hours: around 2000 Cost of excavator operating hour: 110 EU

210.000,00 Operating hour cost comprises the fol-lowing expenses: amortization and loan, work force, energy substances, servicing, admini-stration costs, insurance, com-pany’s profit

3. Annual profit assessment 10% of profit 21.000,00 Loss review 1. Lost income during the

litigation (IP) 4 months 70.000,00

2. Lost profit during the

litigation (ID) 4 months 7.000,00

3. Work force costs during the

litigation (TR) 4 months 6.000,00

4 month long litigation

4. Cost of replaced parts due to wear caused by oil contamination (TI)

198.456,00 Manufacturer covered the costs

5. Cost of upgrading the filter-ing system (TF)

7.945,00 Manufacturer covered the costs

6. Litigation expenses (oil change, examination, servicing the hammer and the excavator, expert’s opinion) (OT)

30.000,00 Manufacturer and user shared the expenses fifty-fifty.

SUMMARY A User’s loss TI + TF+ 0,5 ⋅ OT 221.401,00 B Manufacturer’s loss ID + TR + 0,5 ⋅ OT 28.000,00

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In the table above, one may see that for the equipment which keeps the contamination level in the hydraulic system at the needed level, it was necessary to allocate only 4% of the total amount that was needed to bring the excavator to the proper operating condition. Since this is a negligible amount compared to the total value of the excavator, the gene-ral conclusion in this analysis would be that for the assets invested in the secondary filtering system that should maintain the level of oil cleanliness at a required level, far more is returned through reliability and efficiency of the excavator during the operation. The best indicator that the applica-tion of diagnostics and the system for keeping the level of contamination at a required level is done properly is the fact that during the exploitation of 4500 operating hours the excavator operated without any failures after the replacement of its hydraulic components.

Conclusion A proper application of diagnostics and appropriate maintenance of

the hydraulic system led to the conclusions as follows: • By applying diagnostics to certain operating parameters of the

hydraulic system (such as pressure, flow, fluid operating temperature, temperature of critical components, etc.) and by monitoring the contami-nation level, it is possible to determine the cause of failures or failures of certain parts in the hydraulic system or the whole system. In addition, with a proper use of certain diagnostic devices, and by knowing the criti-cal points in the system, the system parts and components working un-der the largest loads can be identified, as well as the values of certain operating parameters that may lead to a failure of a component,

• By constantly monitoring the operating parameters in the hydraulic system and a level of contamination through automatic control, it is pos-sible to forecast adequately and act preventively in order to remove the potential causes of system failure,

By an appropriate replacement and a proper choice of critical parts in the hydraulic system, the overall reliability of the hydraulic system is upgraded as well as the productivity and efficiency of the system,

• With minimum investments in corresponding equipment for kee-ping the contamination level in the hydraulic system, multiple expenses of hydraulic system maintenance are decreased, providing a proper and long-lasting operation of the hydraulic system.

In conclusion, it can be said that for maintaining a hydraulic system it is necessary to apply certain diagnostic measures during the opera-tion of a modern hydraulic system, as well as appropriate systems for keeping the pureness of the working fluid at the level required for pro-

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per operation of the system. The symbiosis between diagnostics and devices for controlling the working fluids, especially hydraulic oils, has been lately recognized as unavoidable and it requires the increasing application and installation of these devices as standard parts in mo-dern machines.

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tornih vozila kao složenog tehničkog sistema. Vojnotehnički glasnik/Military Tec-hnical Courier, 57(2), pp. 31-45.

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OTKAZ HIDRAULIČNOG SISTEMA ČEKIĆA KAO POSLEDICA KONTAMINACIJE ČVRSTIM ČESTICAMA

OBLAST: mašinstvo TIP ČLANKA: originalni naučni članak

Rezime:

Hidraulični sistemi mobilnih mašina su često kontaminirani čvrstim česticama. Čvrste čestice povećavaju intenzitet abrazivnog habanja hi-drauličnih komponenata, i čine jednim od glavnih uzročnika otkaza si-stema. U radu je dat prikaz reprezentativnog primera uticaja čvrstih če-stica na povećano habanje delova hidrauličnog čekića bagera u eks-ploatacionim uslovima bagera u cementnoj industriji.

Uvod Kontaminacija radnog fluida hidrauličnog sistema, jedan je od najve-

ćih neprijatelja mobilnih mašina. Na mobilnim mašinama, koje se obično koriste u kontaminiranoj sredini, potrebno je pravilnim projektovanjem zaš-tititi hidraulični sistem posebno od eksterne kontaminacije. Uticaj kontami-nanata na rad i pouzdanost hidrauličnih komponenata, a time i hidrauličnih sistema, može značajno da smanji planirani eksploatacioni vek.

U radu je dat prikaz uticaja kontaminacije radnog fluida hidraulič-nog sistema bagera preko radnog dela, hidrauličnog čekića. Uočeno je da zbog loše konstrukcije čekića i nepravilnog izbora povratnog filtera u hidrauličnom sistemu bagera, u toku rada dolazi do prodora konta-minanata u vidu čvrstih čestica koje dovode do povećanja habanja radnih delova hidrauličnih komponenata (prvenstveno pogonske hidra-ulične pumpe) kao i radnih delova hidrauličnog čekića. Da bi se shvatio uticaj kontaminacije hidrauličnog ulja čvrstim česticama, u radu je pri-ložena foto-dokumentacija kritičnih delova pojedinih komponenti koje su oštećene. Takođe, izvršena je ekonomska analiza koja ukazuje na potrebu da se na mobilnim mašinama izvrši adekvatno filtriranje hi-drauličnog fluida.

Opis rada hidrauličnog sistema čekića Dat je opis jednog radnog ciklusa hidrauličnog čekića. Radni pro-

ces izazivanja udaraca čekićem zahteva kontinualno ponavljanje pret-hodno opisanog ciklusa. Iz navedenog se vidi da je rad hidrauličnog če-kića veoma dinamičan ciklus kretanja određenih delova čekića, koji da bi ispravno radili zahtevaju i određene uslove za dugotrajnu ekspolataciju. Jedan od tih uslova je i održavanje radnog fluida čistim.

Uzročnici kontaminacije na hidrauličnom sistemu bagera Priložena fotodokumentacija daje prikaz jednog od glavnih uzročnika

povećane koncentracije kontaminanat u fluidu – neispravan filterski ulo-žak, koji se usled cikličnih opterećenja habao i nije vršio zadatu funkciju.

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Uticaj kontaminanata na oštećenje hidrauličnih komponenata bagera Na priloženim slikama uočavaju se tragovi abrazivnog habanja kao

glavne vrste trošenja radnih elemenat hidrauličnog čekića, koji su nastali kao posledica prodora ogromne količine kontaminanata u vidu čvrstih čestica cementne i betonske prašine u hidraulični sistem bagera.

Monitoring hidrauličnog sistema čekića U hidrauličnom sistemu bagera i radnog sklopa – hidrauličnog če-

kića, uz pomoć uređaja za snimanje čvrstih čestica u radnom fluidu, ot-kriveni su glavni uzročnici kontaminacije koji su dovodili do relativno br-zog zastoja hidrauličnog sistema i čekića.

Tehno ekonomska analiza nastale havarije Iz izvedene analize se vidi da je za opremu kojom se održava ni-

vo kontaminacije u hidrauličnom sistemu na potrebnom nivou neop-hodno izdvojiti svega 4% od ukupne sume koja je bila potrebna da se bager dovede u ispravno stanje. Kako je ovo zanemariva cifra u odno-su na ukupnu vrednost bagera, opšti zaključak u ovoj analizi je da se za uložena sredstva u sekundarni sistem filtriranja kojim se postiže ni-vo održavanja uljnog punjenja na potrebnom nivou, daleko više vraća kroz pouzdanost i efikasnost bagera u toku rada.

Zaključak Pravilna primena dijagnostike i odgovarajuće održavanje hidrau-

ličnog sistema ukazuje na sledeće zaključke: – Određenim dijagnostičkim uređajima i njihovom pravilnom prime-

nom i poznavanjem kritičnih tačaka u sistemu mogu se utvrditi delovi i komponente u sistemu koji podnose najveća opterećenja kao i vrednosti određenih radnih parametara koji mogu dovesti do zastoja ili otkaza komponente,

– stalnim praćenjem radnih parametara u hidrauličnom sistemu i nivoa kontaminacije putem automatske kontrole, moguće je na adekva-tan način predvideti i preventivno delovati kako bi se otklonile potencijal-ni uzroci otkaza sistema,

– odgovarajućom zamenom i pravilnim izborom kritičnih delova u hidrauličkom sistemu, povisuje se ukupna pouzdanost hidrauličnog si-stema kao i produktivnost i efikasnost sistema,

– uz minimalna ulaganja u odgovarajuću opremu za održavanje ni-voa kontaminacije u hidrauličnom sistemu, smanjuju se višestruki troš-kovi održavanja hidrauličnog sistema i obezbeđuje pravilan i dugotrajan rad hidrauličnog sistema.

Ključne reči: čvrste čestice, bageri, hidraulika, habanja.

Datum prijema članka/Paper received on: 16. 10. 2013. Datum dostavljanja ispravki rukopisa/Manuscript corrections submitted on: 02. 11. 2013. Datum konačnog prihvatanja članka za objavljivanje/ Paper accepted for publishing on: 04. 11. 2013.

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